Animal Model and Molecular Interactions of Cln5

Neuronal ceroid lipofuscinoses (NCLs) are a family of inherited pediatric neurodegenerative disorders, with an incidence of 1:12 500 in the US and Scandinavian countries and 1:100 000 worldwide. The major hallmarks of NCLs include retinal degeneration, death of selective neuronal populations and accumulation of autofluorscent ceroid-lipopigments. The clinical manifestations are generally similar in all forms. The Finnish variant late infantile neuronal ceroid lipofuscinosis (vLINCLFin) is a form of NCL, especially enriched in the Finnish population. The clinical symptoms include motor clumsiness, progressive retinal degeneration, motor and mental deterioration, myoclonia and seizures. The first aim of this thesis was to analyse the brain pathology of vLINCLFin utilising the novel Cln5-/mouse model. The Cln5-/mouse presented with the classical hallmarks of the vLINCLFin pathology, including autofluorescence and typical ultrastructure of the storage deposits in brains of the affected mice and therefore, proved to be an excellent model to study vLINCLFin. Gene expression profiling of the brains of already symptomatic Cln5-/mice revealed that inflammation, neurodegeneration and defects in myelinization are the major characteristics of the later stages of the disease. Histological characterization of the brain pathology confirmed that the thalamocortical system is affected in Cln5-/mice, being consistent with the findings from other NCL mouse models. Whereas the brain pathology in all other analyzed NCL mice initiate in the thalamus and spread only months later to the cortex, we observed that the sequence of events is uniquely reversed in Cln5-/mice; the neurodegeneration begins in the cortex and becomes evident in the thalamus only months later. We could also show that even though neurodegeneration is inititated in the cortex, reactive gliosis and loss of myelin are evident in specific nuclei of the thalamus already in the 1 month old brain. To obtain a deeper insight into the disturbed metabolic pathways early in the course of the disease, we performed gene expression profiling of the mouse brains. We substantiated these findings with immunohistological analyses, and could demonstrate that cytoskeleton and myelin were affected in Cln5-/mice. Comparison of gene expression profiling of two NCL mouse models further highlighted that the Cln5-/and Cln1-/mice share a common defective pathway, leading to disturbances in the neuronal growth cone and cytoskeleton. Encouraged by the first evidence of common pathogenetic mechanisms behind two forms of NCL, we systematically analyzed the molecular interactions of NCLproteins and observed that Cln5 and Cln1/Ppt1 proteins interact with each other. Furthermore, we demonstrated that Cln5 and Cln1/Ppt1 share an interaction partner, the F1-ATP synthase, potentially linking both LINCLFIN and INCL diseases to disturbed lipid metabolism. In addition, Cln5 was also shown to interact with other NCL proteins; Cln2, Cln3, Cln6 and Cln8 implicating a central role for Cln5 in the NCL pathophysiology. This study is the first to describe the brain pathology and gene expression changes in the Cln5-/mouse. Together the findings presented in this thesis represent novel information of the disease processes and the molecular mechanisms behind vLINCLFin and have highlighted that the relatively rare Finnish CLN5/vLINCLFin forms a very important model to analyze the pathophysiology of NCL diseases, protein interactome and effects between genes and proteins leading to neurodegeneration in general.